For the past couple of months, I have been working on the replacement of my deck. From dismantling the existing deck, building and improved foundation, installing the new deck and adding new trim pieces (railing, stairs, garden spaces and artwork), my wife and I have done it all of the work. Now, as I am finishing up the final details, I get to start on an other interesting project. For years, I have wanted to build a smart solar lighting system. My plan is to build a pair of solar powered lamps to highlight the stairs leading from the deck to the backyard. The idea is to utilize the space between the pair of posts on either side of the stair opening. The spacing between the posts is ~6 1/4", and it will illuminate in both directions.
The LED lights will fit between the posts and directly under the deck railing cap. Here are some pictures of the first prototype of the light enclosure:
In the second image, the light is being illuminated by a pair of LEDs that are plugged into a protoboard and powered by a Li-Ion battery (board and wires are visible behind the glass). With the obvious bright spots in the image, it is apparent that a good diffuser is going to be necessary to create a more uniform light pattern. This weekend I ordered a bunch of plexiglass samples to try and find an appropriate diffuser, trying to strike the correct balance of diffusion versus opacity (I don't want to waste my precision illumination). Along with the diffuser, I am planning on embedding the battery, electronics and the diffuser inside a plexiglass tube, which will be centered behind the pair of glass panels (plexiglass tubing and rubber endcaps were a part of the order). A solar panel will be attached to the deck railing above each light fixture (this will not provide optimum solar exposure, but I am hopeful that I can capture enough solar energy to recharge the Li-Ion battery).
The features of my smart solar LED light fixture includes:
- Li-Ion charger, with programmable charging current level to find the maximum power point (as opposed to true power point, I will be stepping up the current as long as the solar panel voltage remains about the battery voltage)
- Li-Ion battery with a capacity of 840 mAh.
- Four Warm LEDs (two facing towards the deck and two facing towards the stairs), providing 17 lm (at 30 mA each) of lighting at both faces (depending on diffuser losses). This capacity should be sufficient to provide ~ 7 hours of illumination, but I plan to run considerably shorter light schedules to hopefully handle a cloudy day or two.
- Real time clock (super capacitor backup) to track time of day and allow programmable light schedules.
- Enocean transceiver to allow communications to a PC-based application providing data collection and time of day synchronization and limited interaction with Enocean switches (semi on-demain lighting).
- Power saving electronics to periodically sleep the Enocean transceiver (quite power hungry for a battery powered application)
- LED current monitoring to adjust lighting based on changes in battery voltage.
- Provisions for solar voltage cut off if unloaded voltage rises above the battery charger maximum input (not needed for the initial design as the selected solar panels are within the safe range on the charger).
- Provision for using the LEDs as a load to the solar panels for characterizing the solar panels prior to final initialization.
I'll be following this up soon, with some of the design choices and other information.